A common method for installing membrane type roofing systems on low sloping roofs employs a lapped configuration of membrane sheets. The portion of each sheet that extends under the next successive sheet is called the “lap edge”. The lap edge is used for securement of the sheet to underlying roof materials such as cover board, etc. typically using mechanical means such as screws and washers to secure the lap edge through the underlying materials into the structural roof deck.
The next successive membrane sheet is then attached to the now secured sheet in a manner that over laps the mechanical fasteners. In many cases the attachment of the overlying sheet will be by welding to the underlying sheet to create a water tight seal between each overlapping sheet of membrane.
While the art recognized method performs well for many conditions, there are wind uplift and other conditions that can cause this type of roof to fail by pulling the mechanical attachments through the material of the lap edge.
There have been attempts to improve this type of system in the past such as reducing the distance between fasteners, using termination bar and welding the roofing material on both sides of the mechanical fasteners. None of these improvements are favored however.
With respect to reducing the distance between fasteners, although it is true that the fasteners are less likely to pull through the membrane, the multiplicity of holes tends to cause a perforated tear-line effect such that the membrane edge is torn away from the membrane body. With respect to termination bar, the product is improved but it does still suffer from the fasteners tearing through the membrane in the shear direction of the membrane. With respect to welding on both sides of the fastener, the finished product works well but getting there is labor intensive and difficult.
Therefore, there still exists a need for improvement in the lap-style roofing assemblies and methods for such assembly.